Fast pyrolysis is a process during which organic carbonaceous biomass feedstock, i.e., “biomass”, such as wood waste, agricultural waste, algae, etc., is rapidly heated to between about 300° and about 900° C. in the substantial absence of oxygen using a pyrolysis reactor. Fast pyrolysis processes include Rapid Thermal Processing (RTP), in which an inert or catalytic solid particulate is used to carry and transfer heat to the feedstock. Under these conditions, solid products, liquid products, and gaseous pyrolysis products are produced. A condensable portion (vapors) of the gaseous pyrolysis products is condensed into biomass-derived pyrolysis oil. Biomass-derived pyrolysis oil can be burned directly as fuel for certain boiler and furnace applications, and can also serve as a potential feedstock in catalytic processes for the production of fuels in petroleum refineries. Biomass-derived pyrolysis oil has the potential to substitute for traditional petroleum-derived transportation fuels, thereby reducing the dependency on conventional sources and reducing the environmental impact.
However, biomass-derived pyrolysis oil is a complex, highly oxygenated organic liquid having properties that currently limit its utilization as a biofuel. For example, biomass-derived pyrolysis oil has high acidity and a low energy density attributable in large part to oxygenated hydrocarbons in the oil, which undergo secondary reactions during storage. “Oxygenated hydrocarbons” as used herein are organic compounds containing hydrogen, carbon, and oxygen. Exemplary oxygenated hydrocarbons produced from pyrolysis include carboxylic acids such as acetic acid, phenols, cresols, and aldehydes such as furfural, levoglucosan, etc. It should be appreciated that while the oil produced according to exemplary embodiments of the present invention is generally described herein as a “low oxygen biomass-derived pyrolysis oil”, this term generally includes any oil produced having a lower oxygen concentration than conventional biomass-derived pyrolysis oil. Conventional biomass-derived pyrolysis oil comprises about 30% by weight oxygen from these oxygenated hydrocarbons. Significant upgrading, however, may be achieved by hydroprocessing of the raw pyrolysis oil. Conversion of biomass-derived pyrolysis oil into biofuels and chemicals requires full or partial deoxygenation of the biomass-derived pyrolysis oil.
Accordingly, it is desirable to provide methods and catalysts for producing purified low-oxygen biomass-derived pyrolysis oils. Such deoxygenation may proceed via two main routes, namely the elimination of either water or CO2 from hydrogenation or decarboxylation, respectively. In the present invention, the pyrolysis oils are hydrotreated to remove the majority of the oxygen. Then the treated pyrolysis oil is treated with ionic liquids to remove the oxygenated hydrocarbons that are resistant to hydrotreating including phenols and similar compounds.
The biomass-derived pyrolysis oils are contaminated with phenols, nitrogen-containing compounds, metals and other undesirable contaminants that interfere with processing to produce higher grade fuels. For example, such contaminants are harmful to hydrocracking catalysts so that it is highly desirable to remove them before hydrocracking. One possible method to remove the nitrogen compounds is by hydrotreating, but it is costly and takes considerable energy. Despite recent progress in the area of biofuel development, however, there remains a need in the art for improved methods of removing contaminants from pyrolysis oil, particularly for phenols. It has now been found that ionic liquids can be used to purify the low-oxygen content biomass-derived pyrolysis oils to remove phenolic compounds and/or nitrogen containing compounds.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims.